Glutamate evoked pertussis toxin-sensitive currents in Xenopus oocytes expressing metabotropic glutamate receptor subtype 1 (mGluR1) and exogenous Gilα. The mGluR1-currents were completely blocked by U-73122, a phospholipase C (PLC) inhibitor and by niflumic acid, a chloride channel blocker. In the oocyte further coinjected with poly(A)+ RNA from the guinea pig cerebellum, the mGluR1-currents were inhibited by U-50488H, an opioid κ-agonist, and this inhibition was blocked by norbinaltorphimine, an opioid κ-antagonist. These findings suggest that the mRNA encoding a novel subtype of opioid κ-receptor which inhibits Gi1-PLC-mediated currents is present in guinea pig cerebellar poly(A)+ fractions.
